Method and controller for low-overhead user equipment measurements

ABSTRACT

An embodiment method includes identifying a plurality of VTP configurations representing allocations of TPs among a plurality of VTPs each having at least one TP. Potential serving VTPs are then identified for a selected UE in a plurality of UEs according to at least one UE centric criterion. The potential serving VTPs are selected for each of the plurality of VTP configurations. A UE measurement set is then scheduled for the potential serving VTPs for a scheduled channel resource according to measurement parameters. The method further includes selecting a serving VTP configuration from the plurality of VTP configurations according to UE measurement feedback from the selected UE.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/620,337, filed on Jun. 12, 2017 and entitled “Method and Controllerfor Low-Overhead User Equipment Measurements,” which claims priority toU.S. patent application Ser. No. 14/528,878, filed Oct. 30, 2014, nowU.S. Pat. No. 9,681,324, entitled “Method and Controller forLow-Overhead User Equipment Measurements,” which applications are herebyincorporated by reference herein as if reproduced in their entireties.

TECHNICAL FIELD

The present invention relates generally to a system and method forlow-overhead user equipment (UE) measurements and, in particularembodiments, to a controller and method for measuring channels between aUE and a plurality of transmit points.

BACKGROUND

A typical wireless network includes many transmit points (TPs) that spana coverage area and can be grouped into one or more coordinating setsreferred to as virtual transmit points (VTPs). A VTP includes one ormore TPs that coordinate according to a protocol, such as dynamic pointselection (DPS) or joint transmission (JT). A TP, sometimes referred toas a cell, is any access point (AP), or sector thereof, for the network.Network communication is further divided into time and frequencyresource blocks. The member TPs of each VTP in the network can varyaccording to demand. For a given resource block, there are one or moreVTP configurations that specify the TP composition of each VTP. A VTPconfiguration is selected for the given resource block according tomeasurements of the channels among the various TPs and user equipments(UEs), where the measurements are made by the UEs and fed back to thenetwork.

A UE is served by a VTP for a given resource block. The VTP that servesa given UE can vary with each resource block. The selection of a VTP toserve the given UE, as well as certain transmission parameters, can bemade according to the measurements of the channels.

UE measurements are made based on a transmission of a pilot from a TP tothe UE. The TP typically broadcasts the pilot toward multiple UEs thatthen make their measurements and report, or feed-back, the results tothe network. UE measurements are typically made at an overhead cost,which includes the network and processing resources required to transmitpilots, make measurements, and transmit the measurements back to thenetwork. The network, typically through a controller, or base station,aggregates the measurements, selects a VTP configuration, andrespectively assigns a VTP to serve each UE. The controller weighs themeasurements against the interference, overhead, and accuracyrequirements for the network.

SUMMARY

Embodiments of the present invention provide a method of selectingrespective serving VTPs to serve a plurality of UEs and a wirelesscommunication system controller for the same.

An embodiment method of selecting a configuration of serving VTPs toserve a plurality of UEs includes identifying a plurality of VTPconfigurations representing respective allocations of TPs among aplurality of VTPs. Each of the plurality of VTPs includes at least oneTP. The method further includes, for each of the plurality of VTPconfigurations, identifying potential serving VTPs for a selected UE inthe plurality of UEs according to at least one UE centric criterion. Thepotential serving VTPs are selected from among the plurality of VTPs foreach of the plurality of VTP configurations. A UE measurement set isthen scheduled for the potential serving VTPs for a scheduled channelresource according to measurement parameters. The method furtherincludes selecting a serving VTP configuration from the plurality of VTPconfigurations according to UE measurement feedback. The UE measurementfeedback is received from the selected UE.

A controller embodiment for a wireless communication system includes amemory, a transceiver, and a processor coupled to the memory and thetransceiver. The wireless communication system includes TPs serving aregion within which a plurality of UEs are disposed. The memory isconfigured to store a plurality of VTP configurations according to whichthe TPs are allocable into a plurality of VTPs. Each of the plurality ofVTP configurations represents an allocation of the TPs. The transceiveris configured to transmit UE measurement instructions to the TPs and aselected UE in the plurality of UEs. The transceiver is also configuredto receive UE measurement feedback from the plurality of TPs and theselected UE. The processor is configured to identify potential servingVTPs for the selected UE according to at least one UE centric criterion.The potential serving VTPs are identified for each of the plurality ofVTP configurations. The processor is also configured to schedule a UEmeasurement set for the potential serving VTPs for a scheduled channelresource according to measurement parameters. The processor is furtherconfigured to generate and cause the transceiver to transmit the UEmeasurement instructions according to the UE measurement set. Theprocessor is further configured to select a serving VTP configurationfrom the plurality of VTP configurations according to UE measurementfeedback received from the selected UE by the transceiver.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a block diagram of one embodiment of a wireless communicationsystem;

FIG. 2 is an illustrative diagram of one embodiment of a wirelessnetwork;

FIG. 3 is an illustrative diagram of an embodiment of a multi-VTPconfiguration wireless network;

FIG. 4 is another illustrative diagram of the multi-VTP configurationwireless network embodiment of FIG. 3 with cell-edge UEs;

FIG. 5 is yet another illustrative diagram of the multi-VTPconfiguration wireless network embodiment of FIG. 3;

FIG. 6 is an illustrative diagram of one embodiment of a resource unitgrid;

FIG. 7 is a flow diagram of one embodiment of a method of measuringchannels between a UE and a plurality of TPs;

FIG. 8 is a flow diagram of another embodiment of a method of measuringchannels between a UE and a plurality of TPs;

FIG. 9 is a block diagram of one embodiment of a wireless communicationsystem;

FIG. 10 is a block diagram of one embodiment of a controller for awireless communication system; and

FIG. 11 is a flow diagram of one embodiment of a method of selectingrespective serving VTPs to serve a plurality of UEs.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of embodiments are discussed in detail below. Itshould be appreciated, however, the present invention provides manyapplications and inventive concepts that may be embodied in a widevariety of specific contexts. The specific embodiments discussed hereinare merely illustrative of specific ways to make and use the invention,and do not limit the scope of the invention.

It is realized herein the overhead used for UE measurements can bereduced with certain measurement techniques that can eliminateredundancies and sacrifice some accuracy when appropriate. It isrealized herein that each UE in a wireless communication systemgenerally receives strong power from a limited number of TPs, which arepotential serving TPs or strong interferers. The UE measurements arefocused on those TPs. Any power received from other TPs is generallyinsignificant relevant to that received from the strong TPs. It isrealized herein the interference from the other TPs can be measured, bythe UE, in the aggregate to approximate a sum interference. It is alsorealized herein that accurate UE measurements are more important whenthe UE is on or near the edge of a cell. When a UE is generally centeredin a cell, the selection of a VTP configuration, VTP, and ultimately aTP to serve the UE is simplified, because of the relatively high powerreceived from the TP centered in the cell. Additionally, it is realizedherein, the rate at which sum interference is measured can be less thanthe rate at which strong TPs are measured by a given UE. It is furtherrealized herein the selection of an update rate for these measurementsin the time and frequency domain can be made according to the rate atwhich the corresponding VTP configuration is selected.

FIG. 1 is a block diagram of one embodiment of a wireless communicationsystem loft Wireless communication system 100 includes a base station nothat serves one or more UEs, such as UE 120, UE 130, UE 140, and UE 150,by receiving communications originating from the UEs and forwarding thecommunications to their respective intended destinations, or byreceiving communications destined for the UEs and forwarding thecommunications to their respective intended UEs. Some UEs cancommunicate directly with one another as opposed to communicatingthrough base station no. For example, in the embodiment of FIG. 1, a UE160 transmits directly to UE 150, and vice versa. Base station no issometimes referred to as an access point, a NodeB, an evolved NodeB(eNB), a controller, or a communication controller. UEs 120 through 160are sometimes referred to as stations, mobile stations, mobiles,terminals, users, or subscribers.

FIG. 2 is an illustrative diagram of one embodiment of a wirelessnetwork 200. Wireless network 200 includes nine cells, or TPs, dividedinto three VTPs: VTP 210, VTP 220, and VTP 230. VTP 210 includes cells0, 1, and 2; VTP 220 includes cells 3, 4, and 5; and VTP 230 includescells 6, 7, and 8. The allocation of the nine cells into the three VTPsis done by a controller for wireless network 200. Alternativeembodiments can include any number of cells. Furthermore, alternativeembodiments can divide those cells among any number, one or more, ofVTPs. When a UE is to be served by wireless network 200, it is served bythe TPs in one of the three VTPs. While being served by one of the VTPs,any signals or noise received by the UE from any VTP not serving the UEis considered interference. For example, in the embodiment of FIG. 2,when a UE is being served by VTP 220, any signal or noise received bythe UE from TPs 0, 1, or 2 in VTP 210, or from TPs 6, 7, or 8 in VTP 230is considered interference.

The selection of a VTP and the TPs within to serve a UE is madeaccording to measurements of the various channels between the UE and theTPs. These measurements are made by the UE, along with any other UEs tobe served by wireless network 200. To measure a channel between a givenTP and the UE, the UE observes transmissions among the various TPs andUEs. Certain measurements are made using known transmissions, or pilots,from the TPs. For example, consider the UE to be served by VTP 220. TheUE measures the respective channels between it and TPs 3, 4, and 5, aswell as any interference from VTPs 210 and 230. One way to measure thechannel between TP 3 and the UE is to instruct TPs 4 and 5 to mute, orto not transmit, and instruct TP 3 to transmit a pilot. The respectivechannels between TPs 4 and 5 and the UE are similarly measured,utilizing three transmissions, or resource units. A resource unit,sometimes referred to as a resource element, is the smallest division oftime and frequency resources allocated for a given wirelesscommunication system. To measure the interference from VTPs 210 and 230,TPs 3, 4, and 5 are instructed to mute and the UE listens for any powerthat leaks from the TPs of VTPs 210 and 230 into the channels for VTP220. The interference measurement is effectively an aggregate of allinterference originating outside VTP 220. The interference measurementutilizes one transmission, or resource unit.

FIG. 3 is an illustrative diagram of one embodiment of a multi-VTPconfiguration wireless network 300. Wireless network 300 includes ninecells divided into at least one VTP. Wireless network 300 includes threeVTP configurations, VTP configuration A, VTP configuration B, and VTPconfiguration C. Each of the three VTP configurations specifies adifferent division, or allocation, of the nine cells among the one ormore VTPs. Alternative embodiments can include any number of VTPconfigurations. VTP configuration A includes the three VTPs of theembodiment wireless network of FIG. 2, VTP 210, VTP 220, and VTP 230.VTP configuration B includes four VTPs: VTP 310, VTP 320, VTP 330, andVTP 340. VTP 310 includes cells 1 and 2. VTP 320 includes cells 3 and 5.VTP 330 includes cells 6 and 7. VTP 340 includes cells 0, 4, and 8. VTPconfiguration C includes three VTPs: VTP 350, VTP 360, and VTP 370. VTP350 includes cells 0, 2, and 5. VTP 360 includes cells 3, 4, and 6. VTP370 includes cells 7, 8, and 1.

For a given UE to be served by wireless network 300, the UE needsmeasurements for the respective channels between it and the TPs withinthe VTP that will serve it, for each VTP configuration. The selection ofVTPs within a given VTP configuration to serve the UE is made accordingto at least one UE centric criterion. UE centric criteria include thelocation of UEs, UE quality of service (QoS), and UE quality ofexperience (QoE). UE centric criteria allow the selection of potentialserving VTPs to be optimized for each UE or group of UEs. The UEmeasurements are then used, along with measurements made by any otherUEs to be served by wireless network 300, to select a VTP configurationto be employed for a given resource block. For example, a UE in theproximity of cell 5 may be served by VTP 220 in VTP configuration A, byVTP 320 in VTP configuration B, or by VTP 350 in VTP configuration C.

UE measurements are made with a certain amount of accuracy and at a costof a certain amount of overhead. The balance of overhead versus accuracyis adjustable through several techniques. The overhead cost of a UEmeasurement is represented as resource units per resource block percell. Variance in the overhead cost is found among the various mutes andpilot transmissions used to make the UE measurements, each of whichconsumes resource units. Additionally, the overhead required for ameasurement is scaled by a parameter, k, according to the number ofantennas and various other parameters for a given TP. The parameter k isthe number of resource units used to properly estimate a channel andrepresents a trade-off between the accuracy of a particular measurementfor one port of a TP and the overhead for the one port. In certainembodiments, for a given VTP configuration, a baseline UE measurementincludes one TP transmitting a pilot and all others muting, consuming 1k resource units per resource block per cell. The measurement isrepeated by the UE for each strong-powered TP. The baseline UEmeasurements also include a sum interference measurement made by mutingall strong-powered TPs and instructing all other TPs to transmit apilot. The UE measures the aggregate power of all weak-powered TPs.

For example, for VTP configuration A of FIG. 3, UE measurements for VTP210, VTP 220, and VTP 230 have an overhead cost of (3+1)k resource unitsper resource block per cell. To arrive at this overhead cost, consider asingle cell, for example cell 3 of VTP 220. A channel between the UE andthe TP 3 is measured along with two others between UE and TP 4 and TP 5.TP 3 is measured by muting TP 4 and TP 5, and transmitting a pilot fromTP 3. Likewise, TP 4 is measured by muting TP 3 and TP 5, andtransmitting a pilot from TP 4; and TP 5 is measured by muting TP 3 andTP 4, and transmitting a pilot from TP 5. That amounts to one pilottransmission and two mutes per cell, giving the 3 k resource units perresource block per cell. Each of TPs 3, 4, and 5 are then muted whileTPs 0, 1, 2, 6, 7, and 8 transmit a pilot, allowing the UE to measurethe sum interference from those TPs. That amounts to one mute per cell,giving the +1 k resource units per resource block per cell. Each of VTP210, VTP 220, and VTP 230 has three cells, so the total overhead cost ofUE measurements for VTP configuration A is nine cells times (3+1)kresource units per resource block. The average overhead cost of UEmeasurements for VTP configuration A is also (3+1)k resource units perresource block.

Now consider VTP configuration B of FIG. 3. VTP 310 consumes (2+1)kresource units per resource block per cell, as do VTP 320 and VTP 330.VTP 340, which has three cells, consumes (3+1)k resource units perresource block per cell. The total overhead cost of UE measurements forVTP configuration B is six cells times (2+1)k resource units perresource block plus three cells times (3+1)k resource units per resourceblock. The average overhead cost of UE measurements for VTPconfiguration B is (2.33+1)k resource unit per resource block per cell.

The overhead costs for baseline UE measurements for VTP configuration Care similar to the costs for VTP configuration A, because, although VTP350, VTP 360, and VTP 370 are distinct from VTP 210, VTP 220, and VTP230, each contains three cells. Accordingly, the average overhead costfor baseline UE measurements for VTP configuration C is (3+1)k resourceunits per resource block per cell.

Certain embodiments use similarities among the various VTPconfigurations to reduce the overhead cost of UE measurements. When aVTP in a second VTP configuration is a subset of another VTP in a firstVTP configuration, the measurements for the first VTP configuration canbe used for the second VTP configuration. For example, in the embodimentof FIG. 3, VTP 310 of VTP configuration B is a subset of VTP 210 of VTPconfiguration A. UE measurements made for cells 1 and 2 for VTPconfiguration A can be reused for VTP configuration B. Additionally, theUE measurement made for cell 0 in VTP configuration A can be combinedwith the sum interference measurement for VTP configuration A and reusedas a sum interference measurement for VTP configuration B. UEmeasurements for VTP configuration A would still have an averageoverhead cost of (3+1)k resource units per resource block per cell,which is the baseline overhead cost. For VTP configuration B, VTP 310,VTP 320, and VTP 330 are respective subsets of VTP 210, VTP 220, and VTP230, and have no overhead cost for reusing UE measurements from VTPconfiguration A. VTP 340 is not a subset of any VTP from VTPconfiguration A and therefore has an overhead cost of (3+1)k resourceunits per resource block per cell. The average overhead cost for UEmeasurements for VTP configuration B are then (1+0.33)k resource unitsper resource block per cell. VTP configuration C has no VTPs that aresubsets of any VTPs in VTP configuration B, therefore no reductions inoverhead are achieved by any similarities between those VTPconfigurations. The average overhead cost for UE measurements for VTPconfiguration C are (3+1)k resource units per resource block per cell.

In certain embodiments, measurements are focused on cell-edge UEs.Cell-edge UEs are those that are scheduled to be located on or nearboundaries between cells within a given VTP. FIG. 4 is an illustrativediagram of the multi-VTP configuration wireless network embodiment ofFIG. 3 with various cell-edge UEs 410. In VTP configuration A, VTP 210has cell-edge UEs at the boundaries between cell 0 and cell 2, betweencell 0 and cell 1, and between cell 1 and cell 2. VTP 220 has cell-edgeUEs at the boundaries between cell 3 and cell 5, between cell 3 and cell4, and between cell 4 and cell 5. VTP 230 has cell-edge UEs atboundaries between cell 6 and cell 8, between cell 6 and cell 7, andbetween cell 7 and cell 8. In VTP configuration B, VTP 310 has acell-edge UE at the boundary of cell 1 and cell 2. VTP 320 has acell-edge UE at the boundary of cell 3 and cell 5. VTP 330 has acell-edge UE at the boundary of cell 6 and cell 7. VTP 340 has cell-edgeUEs at the boundaries between cell 0 and cell 4, between cell 0 and cell8, and between cell 4 and cell 8. In VTP configuration C, VTP 350 hascell-edge UEs at boundaries between cell 0 and cell 2 and between cell 0and cell 5. VTP 360 has cell-edge UEs at boundaries between cell 3 andcell 4 and between cell 4 and cell 6. VTP 370 has cell-edge UEs atboundaries between cell 7 and cell 8 and between cell 1 and cell 8.

For VTP configuration C, the overhead cost of UE measurements can bereduced by only carrying out UE measurements for TPs on either side ofthe cell-edge. For example, for VTP 350, the cell-edge UE at theboundary between cell 0 and cell 2 can make UE measurements for cell 0and cell 2, and can ignore any interference from cell 5. Likewise, forthe cell-edge UE at the boundary between cell 0 and cell 5, UEmeasurements can be made for cell 0 and cell 5, and any interferencefrom cell 2 can be ignored. The overhead cost for UE measurements forVTP configuration C are then six times (2+1)k resource units perresource block. The average overhead cost for UE measurements is(1.33+0.66)k resource units per resource block per cell.

In certain embodiments, the frequency at which certain TPs are measuredis set according to their respective significance to the measuring UE.For example, strong TPs that are more likely to serve the measuring UEare measured more frequently than those that are weak. The overhead costof UE measurements for the weaker TPs can be reduced by making the suminterference measurements less frequently. For example, in FIG. 4, UE410 on the boundary between cell 3 and cell 5 in VTP configuration A ismore likely to be served by VTP 220 than VTP 210 or VTP 230. That UE, aswell as other UEs in that proximity, could make UE measurements forcells within VTP 220 more frequently than for cells within VTP 210 orVTP 230. The average overhead cost for baseline UE measurements for VTP220 are (3+1)k resource units per resource block per cell. The reducedmeasurement rate impacts the +1 k resource units per resource block percell allocated for sum interference measurements. The reduction isrepresented as a scalar, a, applied to the +1 k resource units perresource block per cell, where α<1.

In multi-VTP configuration wireless networks, occasionally certain VTPconfigurations are selected more frequently than others. In certainembodiments, the respective rate, in the time or frequency domain, atwhich UE measurements are carried out for various VTP configurationsvaries according to how frequently those VTP configurations areselected. For example, in the embodiment of FIG. 4, VTP configuration Amay be selected 90% of the time, while VTP configuration B and VTPconfiguration C are each selected around 5% of the time. In that case,the frequency at which VTP configuration B and VTP configuration C aremeasured can be reduced. In some embodiments, the frequency reductioncan be a function of the fraction of times one VTP configuration isselected normalized to the most selected VTP configuration. Continuingthe example above, if VTP configuration B is selected 5% of the time andVTP configuration A 90%, the frequency could be reduced by 0.05/0.9. Thereduced overhead cost of UE measurements due to the frequency reductionis represented as a scalar applied to average overhead cost for a givenVTP configuration. VTP configuration C has an average overhead cost of(3+1)k resource units per resource block per cell for baseline UEmeasurements. The average overhead cost with a reduction in thefrequency at which VTP configuration C is measured is 0.05/0.9·(3+1)kresource units per resource block per cell.

FIG. 5 is another illustrative diagram of the multi-VTP configurationwireless network embodiment of FIG. 3 and FIG. 4. Wireless network 500includes a VTP configuration A and a VTP configuration B. VTPconfiguration A includes VTP 210, VTP 220, and VTP 230 of FIGS. 2, 3,and 4. VTP configuration B includes VTP 310, VTP 320, VTP 330, and VTP340 of FIGS. 3 and 4. Wireless network 500 is serving three groups ofUEs, UEs 510, UEs 520, and UEs 530. A group of UEs is one or more UEs.UEs 510 are located in cell 0, UEs 520 are located in cell 4, and UEs530 are located in cell 8.

In certain embodiments, overheard pilots from one VTP configuration canbe used in another VTP configuration to improve accuracy or to reduceoverhead. For example, in the embodiment of FIG. 5, UEs 510 in cell 0would be scheduled to make UE measurements for VTP 210 in VTPconfiguration A. In addition to receiving pilots from the TPs for cells0, 1, and 2, UEs 510 can also overhear pilots transmitted from cell 4and cell 8 when measurements are made for VTP configuration A.Similarly, UEs 520 can overhear pilots from cell 0 and cell 8, and UEs530 can overhear pilots from cell 4 and cell 0. These overheard pilotscan be used for UE measurements for VTP 340 of VTP configuration B. UEmeasurements can use the overheard pilots in a variety of ways,generally to increase the accuracy of UE measurements for VTPconfiguration B or to reduce the rate, in the time or frequency domain,of UE measurements for VTP configuration B. Overheard pilots canincrease accuracy of VTP configuration B UE measurements by providingadditional data points for the baseline UE measurements. Accordingly,the UE measurement rate can be adjusted to achieve the desired balanceof accuracy and overhead cost for UE measurements. Gains in accuracy dueto the overheard pilots can be offset by reducing the UE measurementrate in either frequency or time domain, or in both.

FIG. 6 is an illustration of one embodiment of a resource unit grid 600.Resource unit grid 600 is two dimensional, having a time axis runninghorizontally, and a frequency axis running vertically. A resourceallocation of one resource unit for a UE measurement is designated by apattern-filled square in resource unit grid 600. In resource unit grid600-A, UE measurements are densely allocated among the resource units.In resource unit grid 600-B, UE measurements are less densely allocatedamong the resource units, relative to resource unit grid 600-A.

In certain embodiments, when one VTP configuration is selected more orless frequently than another, the density of resource allocations for UEmeasurements for a given VTP configuration can be adjusted according tohow frequently the given VTP configuration is selected. For example, inthe embodiment of FIG. 6, resource unit grid 600-A illustrates apossible resource allocation, and resource unit grid 600-B illustratesanother. Resource allocations may also be referred to as pilot/mutepattern densities. Resource unit grid 600-A may represent a VTPconfiguration A, and resource unit grid 600-B may represent a VTPconfiguration B. The density of resource allocations in resource unitgrid 600-A relative to resource unit grid 600-B suggests that VTPconfiguration A is selected more frequently than VTP configuration B. Inthe time domain, one of every two resource units is allocated for UEmeasurements for VTP configuration A. One of every three resource unitsis allocated for UE measurements for VTP configuration B. In thefrequency domain, one of every three resource units is allocated for UEmeasurements for VTP configuration A, while one of every four resourceunits is allocated for UE measurements for VTP configuration B.

FIG. 7 is a flow diagram of one embodiment of a method of measuringchannels between a UE and a plurality of TPs. The method begins at astart step 710. At a first individual measurement step 720, at least oneUE is employed to measure the channels of potential serving TPs for afirst VTP configuration. A UE typically receives strong power fromseveral TPs, which are the potential serving TPs. All other TPs arepotential interferers. Measuring the channels for one potential servingTP in the first VTP configuration generally includes instructing the onepotential serving TP to transmit a pilot and instructing the otherpotential serving TPs in the first VTP configuration to mute, ortransmit nothing. This is then repeated for each potential serving TP inthe first VTP configuration.

At a first sum interference measurement step 730, the one or more UEsare employed to measure sum interference for the potential interfererTPs for the first VTP configuration. A UE generally receivesinsignificant amounts of power from the respective potential interfererTPs. The sum interference measurement aggregates all interference into asingle interference measurement. The sum interference measurement ismade by instructing all potential serving TPs in the first VTPconfiguration to mute, allowing the UE to measure the aggregate powerreceived from the potential interferer TPs.

The UE measurements are then repeated for a second VTP configuration. Ata second individual measurement step 740, the at least one UE isemployed to measure the channels of potential serving TPs for the secondVTP configuration. At a second sum interference measurement step 750,the at least one UEs are employed to measure the sum interference forthe potential interferer TPs for the second VTP configuration. Themethod then ends at an end step 760.

FIG. 8 is a flow diagram of another embodiment of a method of measuringchannels between a UE and a plurality of TPs. The plurality of TPs isdivided into one or more VTPs. The allocation of TPs to VTPs can be donein a variety of ways, each different allocation is a different VTPconfiguration. The method begins at a start step 810. At a baseline step820, baseline UE measurements are made by a UE for a first VTPconfiguration. Baseline UE measurements provide a baseline level ofaccuracy at a baseline overhead cost. At a step 830, the overhead costof UE measurements can be reduced relative to the baseline overhead. Atstep 830, similarities between the first VTP configuration and a secondVTP configuration are used to reduce the UE measurements needed for thesecond VTP configuration. For VTPs in the second VTP configuration thatare subsets of a VTP in the first VTP configuration, UE measurements forthe first VTP configuration can be used for the second VTPconfiguration. In alternative embodiments, step 830 is omitted in favorof another technique for balancing accuracy and overhead.

At a step 840, UE measurements are focused on cell-edge UEs to reduce UEmeasurement overhead. By reducing the UE measurements for non-cell-edgeUEs, the accuracy of the UE measurements is reduced. In alternativeembodiments, step 840 can be omitted in favor of another technique forbalancing accuracy and overhead. Focusing on cell-edge UEs can be usedin combination with baseline UE measurements and the technique of step830.

At a step 850, UE measurement overhead is reduced by reducing the rateat which a given UE measures less significant TPs, particularly thosethat are potential interferers, which are measured via a suminterference measurement. The reduced UE measurement rate also reducesaccuracy of those measurements; however, the accuracy is moresignificant for potential serving TPs. The UE measurement rate for suminterference measurements is set according to the desired accuracy forsum interference measurements and according to the acceptable overheadcost for those UE measurements. Alternative embodiments may omit step850 in favor of another technique for balancing accuracy and overhead.

At a step 860, the rate at which UE measurements are made is adjusted,in the time domain, the frequency domain, or in both, according to theselection rate for a given VTP configuration. VTP configurations thatare selected more frequently are measured more frequently, while VTPconfigurations that are selected less frequently are measured lessfrequently. For a VTP configuration that is selected more frequently,the pilot/mute pattern density in the frequency domain or the pilot/mutepattern density in the time domain can be increased to increase theaccuracy of UE measurements for that VTP configuration. An increasedtime domain or frequency domain pilot/mute pattern density causes anincrease in overhead cost. For a VTP configuration selected lessfrequently, the pilot/mute pattern density in the frequency domain orthe pilot/mute pattern density in the time domain can be reduced toreduce the overhead of those UE measurements. Additionally, the reducedpilot/mute pattern density causes a reduced accuracy for the UEmeasurements. The precise ratio of UE measurement rates is set accordingto the accuracy and overhead requirements for the wireless network. Inalternative embodiments, step 860 can be omitted in favor of anothertechnique for balancing accuracy and overhead.

At a step 870, pilots overheard while measuring the first VTPconfiguration are used for measurements for the second VTPconfiguration. The overheard pilots can be used to increase the accuracyof measurements in for the second VTP configuration. The overheardpilots also allow for a reduced measurement rate for the second VTPconfiguration, thereby reducing the overhead for UE measurements for thesecond VTP configuration. Alternative embodiments may omit step 870 infavor of other techniques for balancing accuracy and overhead. Themethod then ends at an end step 880.

FIG. 9 is a block diagram of one embodiment of a wireless communicationsystem 900. Wireless communication system 900 includes a controller 910,a plurality of TPs 920-1 through 920-10, and a UE 930. TPs 920-1 through920-10 cover a region within which UE 930 is disposed. TPs 920-1 through920-10 can be partitioned into one or more VTPs. The partitioning iscarried out by controller 910 according to one or more VTPconfigurations. Controller 910 selects a VTP configuration forpartitioning TPs 920-1 through 920-10 into VTPs according tomeasurements made by UE 930, among a variety of other possibleparameters. UE 930 is configured to make UE measurements for channelsbetween it and TPs 920-1 through 920-10.

To make UE measurements, controller 910 instructs each of TPs 920-1through 920-10 to either transmit a pilot or mute. Controller 910 alsoinstructs UE 930 as to which of TPs 920-1 through 920-10 aretransmitting a pilot and which are muting. Transmitting TPs broadcast apilot for UE 930 to receive and use to measure the channel between UE930 and that TP. To measure one channel, controller 910 instructs onepotential serving TP to transmit a pilot and instructs all otherpotential serving TPs to mute. Potential serving TPs are those fromwhich UE 930 receives strong power, which are typically the nearest TPs.In the embodiment of FIG. 9, the potential serving TPs are TP 920-4, TP920-5, TP 920-6, and TP 920-7. This procedure is then repeated for eachof the potential serving TPs. To measure interference, controller 910instructs all potential serving TPs to mute and all potential interfererTPs to transmit. The potential interferer TPs in the embodiment of FIG.9 are TP 920-1, TP 920-2, and TP 920-3, and TP 920-8, TP 920-9, and TP920-10. UE 930 then makes a sum interference measurement that representsan aggregate signal from all potential interferer TPs.

FIG. 10 is a block diagram of one embodiment of a controller 1000 for awireless communication system. Controller 1000 includes a processor1010, a memory 1020, and a transceiver 1030, all coupled to a data bus1040. Processor 1010 is configured to access memory 1020 through databus 1040, allowing it to cause data to be written and read from memory1020. Processor 1010 is further configured to cause data to betransmitted and received through transceiver 1030. Transceiver 1030serves as an interface to a wireless communication network, which caninclude one or more TP and one or more UE. Transceiver 1030, in certainembodiments, can include its own dedicated memory and processor forimplementing various communication protocols, as well as a networkinterface. The network interface includes a physical connection orwireless connection via one or more antenna.

Memory 1020 is configured to store at least one VTP configurationaccording to a VTP configuration data structure. In the embodiment ofFIG. 10, memory 1020 is configured to store three VTP configurations: aVTP configuration 1 1050-1, a VTP configuration 2 1050-2, and a VTPconfiguration 3 1050-3. Each VTP configuration describes a partition ofthe various TPs in the wireless communication system into one or moreVTP. Processor 1010 is configured to make the partitions for the variousVTP configurations and cause them to be written to memory 1020 accordingto the VTP configuration data structure. The number of TPs in a givenVTP can vary per VTP. The number of VTPs in a VTP configuration can varyper VTP configuration. The number of VTP configuration created for agiven wireless communication system can vary per system and per resourceblock.

Processor 1010 is tasked with selecting a VTP configuration to serve theactive UEs in the wireless communication system for each resource block.The VTP configuration chosen can vary per resource block. The VTPconfiguration selection is made according to a variety of parameters,including UE measurements made for the respective channels between theUEs and the various TPs that make up wireless communication system.Processor 1010 schedules the UE measurements for each resource block.Processor 1010 causes transceiver 1030 to transmit various instructionsto the TPs and the UEs. Instructions to the TPs are typically to eithertransmit a pilot or to mute. The pilot is a sequence used for estimatingchannels and is unique to a given UE. Each UE can have one or moreunique pilots. Instructions to the UEs inform the UEs of when pilots arescheduled to be transmitted, allowing the UEs to make the relevant UEmeasurements. The UEs receive the pilots and measure their respectivechannels, defined in the frequency and time domains. The UEs thentransmit the measurements back to controller 1000. Processor 1010receives the UE measurements for a given resource block throughtransceiver 1030.

FIG. 11 is a flow diagram of one embodiment of a method of selectingrespective serving VTPs to serve a plurality of UEs. The method beginsat a start step 1110. At a forming step 1120, a controller forms aplurality of VTP configurations. Each of the plurality of VTPconfigurations represents an allocation of TPs among a plurality ofVTPs. Each of the plurality of VTPs includes at least one TP. At anidentifying step 1130, potential serving VTPs for each of the pluralityof UEs are identified according to at least one UE centric criterion.The potential serving VTPs are selected from among the plurality of VTPsfor each of the plurality of VTP configurations. UE centric criterioncan include UE location, UE QoS, and UE QoE, among others.

A UE measurement set is scheduled for a scheduled channel resource at ascheduling step 1140. The UE measurement set is scheduled according tomeasurement parameters. Measurement parameters can include similaritiesamong the plurality of VTP configurations, the importance of each of theUEs, the importance of each of the plurality of VTP configurations, andthe relative power received from potential interferer TPs.

The UE measurement set is communicated to the plurality of UEs as UEmeasurement instructions. The plurality of UEs carry out the UEmeasurement set and provide UE measurement feedback to the controller.At a selection step 1150, the controller selects a serving VTPconfiguration from the plurality of VTP configurations according to theUE measurement feedback. By selecting the serving VTP configuration, thecontroller also selects the potential serving VTPs for the serving VTPconfiguration as the respective serving VTPs for the plurality of UEs.The method then ends at an end step 1160.

While this invention has been described with reference to illustrativeembodiments, this description is not intended to be construed in alimiting sense. Various modifications and combinations of theillustrative embodiments, as well as other embodiments of the invention,will be apparent to persons skilled in the art upon reference to thedescription. It is therefore intended that the appended claims encompassany such modifications or embodiments.

What is claimed is:
 1. A method comprising: receiving, by a userequipment (UE), first density information of a first plurality ofresource blocks for a first reference signal; receiving, by the UE, thefirst reference signal in the first plurality of resource blocks havinga first density in frequency domain in accordance with the first densityinformation; performing, by the UE, a first channel measurement inaccordance with the first reference signal received in the firstplurality of resource blocks having the first density; receiving, by theUE, second density information of a second plurality of resource blocksfor a second reference signal; receiving, by the UE, the secondreference signal in the second plurality of resource blocks having asecond density in the frequency domain in accordance with the seconddensity information; and performing, by the UE, a second channelmeasurement in accordance with the second reference signal received inthe second plurality of resource blocks having the second density, thefirst density of the first plurality of resource blocks being differentfrom the second density of the second plurality of resource blocks inthe frequency domain.
 2. The method of claim 1, wherein the firstdensity of the first plurality of resource blocks is adjusted in thefrequency domain according to a selection frequency of a wirelessvirtual transmit point (VTP) configuration.
 3. The method of claim 2,wherein the first density of the first plurality of resource blocks isreduced in the frequency domain in response to the wireless VTPconfiguration being selected more frequently.
 4. The method of claim 2,wherein the first density of the first plurality of resource blocks isincreased in the frequency domain in response to the wireless VTPconfiguration being selected less frequently.
 5. The method of claim 1,wherein the first density information is further used to determine athird density of the first plurality of resource blocks in time domain,and the second density information is further used to indicate a fourthdensity of the second plurality of resource blocks in the time domain.6. The method of claim 5, wherein the third density of the firstplurality of resource blocks and the fourth density of the secondplurality of resource blocks are different in the time domain.
 7. Anapparatus comprising: a processor; and a non-transitory computerreadable storage medium storing programming for execution by theprocessor, the programming including instructions to: receive firstdensity information of a first plurality of resource blocks for a firstreference signal; receive the first reference signal in the firstplurality of resource blocks having a first density in frequency domainin accordance with the first density information; perform a firstchannel measurement in accordance with the first reference signalreceived in the first plurality of resource blocks having the firstdensity; receive second density information of a second plurality ofresource blocks for a second reference signal; receive the secondreference signal in the second plurality of resource blocks having asecond density in the frequency domain in accordance with the seconddensity information; and perform a second channel measurement inaccordance with the second reference signal received in the secondplurality of resource blocks having the second density, the firstdensity of the first plurality of resource blocks being different fromthe second density of the second plurality of resource blocks in thefrequency domain.
 8. The apparatus of claim 7, wherein the first densityof the first plurality of resource blocks is adjusted in the frequencydomain according to a selection frequency of a wireless virtual transmitpoint (VTP) configuration.
 9. The apparatus of claim 8, wherein thefirst density of the first plurality of resource blocks is reduced inthe frequency domain in response to the wireless VTP configuration beingselected more frequently.
 10. The apparatus of claim 8, wherein thefirst density of the first plurality of resource blocks is increased inthe frequency domain in response to the wireless VTP configuration beingselected less frequently.
 11. The apparatus of claim 7, wherein thefirst density information is further used to determine a third densityof the first plurality of resource blocks in time domain, and the seconddensity information is further used to indicate a fourth density of thesecond plurality of resource blocks in the time domain.
 12. Theapparatus of claim 11, wherein the third density of the first pluralityof resource blocks and the fourth density of the second plurality ofresource blocks are different in the time domain.
 13. A computer programproduct comprising a non-transitory computer readable storage mediumstoring programming, the programming including instructions to: receivefirst density information of a first plurality of resource blocks for afirst reference signal; receive the first reference signal in the firstplurality of resource blocks having a first density in frequency domainin accordance with the first density information; perform a firstchannel measurement in accordance with the first reference signalreceived in the first plurality of resource blocks having the firstdensity; receive second density information of a second plurality ofresource blocks for a second reference signal; receive the secondreference signal in the second plurality of resource blocks having asecond density in the frequency domain in accordance with the seconddensity information; and perform a second channel measurement inaccordance with the second reference signal received in the secondplurality of resource blocks having the second density, the firstdensity of the first plurality of resource blocks being different fromthe second density of the second plurality of resource blocks in thefrequency domain.
 14. The computer program product of claim 13, whereinthe first density of the first plurality of resource blocks is adjustedin the frequency domain according to a selection frequency of a wirelessvirtual transmit point (VTP) configuration.
 15. The computer programproduct of claim 14, wherein the first density of the first plurality ofresource blocks is reduced in the frequency domain in response to thewireless VTP configuration being selected more frequently.
 16. Thecomputer program product of claim 14, wherein the first density of thefirst plurality of resource blocks is increased in the frequency domainin response to the wireless VTP configuration being selected lessfrequently.
 17. The computer program product of claim 13, wherein thefirst density information is further used to determine a third densityof the first plurality of resource blocks in time domain, and the seconddensity information is further used to indicate a fourth density of thesecond plurality of resource blocks in the time domain.
 18. The computerprogram product of claim 17, wherein the third density of the firstplurality of resource blocks and the fourth density of the secondplurality of resource blocks are different in the time domain.